Cathode ray tube



F b. 14, 1939. KNOLL 2,147,372

CATHODE RAY TUBE Filed March 14, 1936 INVENTOR. MAX KNOLL BY w m ATTORNEY.

Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE CATHODE. RAY TUBE Max Knoll, Berlin, Ge

rmany, assignor to Tele- Germany Application March 14, 1936,. Serial No. 68,969

In Germany 2 Claims.

In cathode ray tubes with oxide cathodes, after the glass vessel has been sealed following the evacuation by the pump, the oxide cathode must be heated to a temperature above 1000 C.,

to obtain the so-called formation of the cathode surface while the normal operating temperature of the formed cathode amounts to only about 850 0. During the formation, barium atoms emerge from the cathode and which will be deposited on the fluorescent screen where they may cause a certain blackening of the fluorescent mass which is detrimental to a proper viewing of the image on the luminous screen. This condition becomes extremely disagreeable in Brauns tubes for television purposes.

In accordance with the invention, this disadvantage of Brauns tubes with oxide cathode is overcome in that the anode opening or another diaphragm opening in the path of the rays is equipped with a shutter arrangement. This arrangement shall also be employed in other cathode ray tubes more especially in the cathode ray scanning means such as in iconoscopes to be employable as television transmitters.

The accompanying drawing shows two embodiments of a cathode ray tube for television equipped with such a shutter arrangement in accordance with the invention. The invention will be best understood byreference to the accompanying figures in which Fig. 1 shows schematically a cathode ray tube arrangement,

Fig. 2 shows one embodiment of my invention,

Fig. 3 shows a further embodiment of my invention, and

Fig. 4 is a partial front View of the arrangement shown in Fig. 3.

In Figure 1, Ill designates a directly heated incandescent cathode; ll represents a Wehnelt cylinder for controlling a brilliancy; and I2 is an anode conductingly connected to a further diaphragm l3 placed in the path of rays. A luminous screen is designated by 14. For the sake of simplicity, the ray concentration devices and deflection arrangements have been omitted from Figure 1.

As shown in Figure 2, the shutter device for the opening of anode IE, or for the opening of the diaphragm [3, may comprise a level plate 15 movable about a small pivot H5 in the direction of the plane of the anode or diaphragm respectively. In Figure 2, the position of plate 15 in which the anode or diaphragm opening is uncovered is shown in dash lines, while the position in which March 14, 1935 the said opening is covered is shown in full line. The shutter can be operated in that the tube is turned about its longitudinal axis.

In the mode of construction of the shutter arrangement shown in two views at right angle to each other in Figure 3, the structure consists of a plate which can be swung about a shaft ll extending parallel to the plane of the diaphragm or anode. To this end, the cover plate 18 has two lugs l9 arranged at right angle to the plane of plate 18. The shaft 17' may likewise be mounted in two lugs 2| formed by bending from the metallic connecting body 20 between the anode I2 and the diaphragm l3. In the structure of Figure 3 the opening and closing of the anode or diaphragm aperture is obtained by tilting the tube.

Instead of utilizing the Weight of the covering plate for moving it as in the aforedescribed examples of embodiment, it may be moved during the forming of the cathode into the position in which it closes the anode or diaphragm aperture, through magnetic action by means of a small iron piece provided thereon, while after completion of the forming it can be so held by means of a spring that it uncovers the said opening.

It is advisable to arrange the shutter device in such a position relative to the pump stem of the tube that after sealing the said pump stem to the high vacuum tube, the anode or diaphragm aperture will be automatically closed due to the weight of the covering plate in accordance with Figure 2 and Figure 3. In this case the forming of the cathode can be carried out without additional manual operations or operating steps and in the same manner as in the case of a tube without shutter device while at the same time avoiding the detrimental eiiects of the barium atoms radiated during the forming.

I claim:

1. A cathode ray tube apparatus including a cathode, an apertured anode and fluorescing screen, a member pivoted about a bearing point on the surface of said apertured anode and normally retained in a position outside of any pro- .g;

jection of said anode aperture on a plane normal to the major axis of the tube, and electromagnetic means located externally of said tube for bringing said pivoted member into a position wherein said member blocks electron passage 0 through said anode aperture during activation of the cathode of said tube.

2. A cathode ray tube apparatus including a cathode, an apertured anode and a fluorescing screen, a plurality of lugs mounted on said anode,

a rod joining said lugs, a member pivoted about said rod, a spring fastened to said member for retaining the member in a position wherein said member is outside of any projection of said anode aperture on a plane normal to the major axis of the tube, and electromagnetic means located externally of said tube for bringing said pivoted member into a position wherein said member blocks electron passage through said anode aperture during activation of the cathode of said tube.

MAX KNOLL. 

